Although not exclusively, said transmission station is preferably located on the ground such that said internal/external communication represents a normal data communication of the ground/air type between the crew of the aircraft and a station located on the ground and is intended, in particular, for air control. The data transmitted during such a ground/air communication is generally encoded and standardized for reasons of optimizing the transmission performance and of interoperability between the crew of the aircraft and the station located on the ground.
It is furthermore known that such a data transmission system generally comprises:                a transmitting/receiving device which is able to transmit outgoing data messages to outside of the aircraft and to receive incoming data messages from outside of the aircraft, said incoming and outgoing messages which pass through said transmitting/receiving device being encoded;        a message management device:                    which is connected to said transmitting/receiving device;            which receives said encoded incoming messages from said transmitting/receiving device and which transmits said encoded outgoing messages to said transmitting/receiving device; and            which comprises an encoding/decoding means able to carry out encoding/decoding, for example of the PER type described below, said encoding/decoding means decoding said encoded incoming messages, in order to form decoded incoming messages, and encoding decoded outgoing messages in order to form said encoded outgoing messages; and                        at least one man/machine interface means:                    a which is connected to said message management device;            which is able to present to an operator the decoded incoming messages, which are output from said message management device and which originate from said transmission station located outside of said aircraft; and            which allows an operator to generate messages representing decoded outgoing messages, which are then transmitted to said message management device and which are to be sent to said transmission station located outside of said aircraft.                        
Because of an increasingly high number of data communications between the ground and aircraft, in particular transport aircraft, the certification authorities (EASA) have imposed [by means of a certification directive (“Certification Review Item: CRI-F26 Issue 03”, dated 30 Jun. 2003) based on the standardized document ED112 (“Minimum operational performance specification for crash protected airborne recorder systems”, March 2003 issue) and a document ED93 (“Minimum aviation system performance specification for CNS/ATM message recording systems”, November 1998)] the recording, in the cockpit voice recorder, of all of the data exchanges between the crew and the ground. This data recording has been made obligatory for any aircraft whose type certification takes place after 1 Jan. 2005.
In order to meet this obligation, it is therefore appropriate to provide means, on board the aircraft, to record said ground/air or internal/external communications (with respect to the aircraft. However, such an arrangement has several disadvantages.
The addition of means is sometimes difficult to implement, and very often expensive and bulky. Moreover, such an addition makes the architecture of said data transmission system more complex.
Furthermore, as the cockpit voice recorder must record a minimum of two hours of communication and as the volume of data to be recorded is very variable depending on the communication between the controllers on the ground and the crew of the aircraft, the storage volume to be provided must be particularly high, which of course has a negative effect on cost and size.